This invention relates to glass compositions and products that are useful, for example, in furniture applications such as table tops or shelving. In such a setting, it is usually desired for the glass to be as free of color as possible so that the glass does not alter the appearance of the furniture, carpets, or other objects viewed through the glass. However, because of the elongated view path, a pronounced color usually shows at the edge of glass that is otherwise considered clear. In conventional clear glass, the edge color is green due to the presence of iron oxide in the glass. Iron oxide is deliberately added to most flat glass, but even when it is not, sufficient amounts to produce a green coloration are usually present as impurities from the raw materials from which the glass is melted. The green edge color may not be compatible with the decor of the room or with the other portions of the furniture of which the glass is a part.
Additionally, with a sheet of ordinary clear glass having typical dimensions of a shelf or a table top, the green color at the edge is very dark and does little to enhance the attractiveness of the piece. Including colorants in the glass can produce tinted glass of blue, gray, bronze, or other colors, but the accompanying reduction of transmittance has the effect of darkening the edge even more, in some cases rendering the edge essentially black. It would be desirable to have available glass that has a colorful but bright edge appearance.
It is known to produce glass that is almost colorless by selecting raw materials that have very little iron and by including cerium oxide in the glass to "decolorize" the remaining traces of iron. Cerium oxide is a powerful oxidizing agent in glass, and its function in decolorized glass is to oxidize the iron to the ferric state, which is a less powerful colorant and which shifts the transmittance spectrum of the glass toward yellow and away from the usual green-blue effect of iron in glass. The edge of this decolorized glass does not have the conventional green color, but it can have a slightly yellow appearance, and the presence of contaminants in the cerium oxide source material can sometimes produce a dull appearance at the edge. Even more objectionable for some intended uses is the fact that the presence of cerium oxide causes fluorescence of the edge portion of the glass under sunlight or certain artificial lighting conditions having a significant ultraviolet component. The fluorescence is exhibited as a vivid violet color at the edge. This is considered by some to be objectionable for color coordination purposes.
Other colorants can be added to glass to produce different colors that dominate over the green color of iron oxide. For example, cobalt oxide is known to produce blue color in glass. These colorants, however, generally reduce the transparency of the glass significantly, which is usually undesirable in a furniture application or the like.
It would be desirable to have available highly transparent glass with a pleasing edge appearance in colors other than green.
U.S. Pat. No. 4,792,536 (Pecoraro et al.) discloses a glass composition that has a blue tint due to a substantial amount of its iron oxide content being in the reduced ferrous state. It is not a high transparency glass, but has transparency to visible light of less than about 75 percent, usually about 70 percent, at standard thicknesses. The glass is also not colorless, having a measurable blue color in transmittance.